Cheap 2.1 speakers for the theremin

Posted: 4/15/2017 2:04:27 PM

From: Athens, Greece

Joined: 2/27/2017

I have my Open.Theremin.V3 for more than a month know, and it is working great. I usually plug it in aux in of a Sony Mini-Hifi system (rated 300 Watt RMS) and it handles theremin signal with no distortion, with every theremin voice I tried (I particularly like harsh Clara-like voice, I think wavetable 4 from Open.Theremin code).

However, I wanted a more portable solution for when I am on the go, so I tried some cheap Logitech z213 2.1 speakers I had lying around (subwoofer of 4 W RMS 2 satellites of 1.5 W RMS). The small subwoofer gives a quite substantial bass side. However, I observe a clipping distortion in every volume level, that ruins every voice except for the very smooth and mellow voice 1.

This distortion is more apparent in the middle of the frequency range, when the response from the small satellites and the subwoofer become equal. However, this distortion is not audible when I play recordings of my theremin tones through the speakers.

This has led me to believe that the signal level of the theremin overwhelms the speaker amplifier. I think of adding an L-pad variable volume control/attenuator to the theremin output. However, the speakers already have inline volume control, and as I mentioned before, distortion is audible in every volume level.

Observing the volume control circuit, I noticed that the line signal is passed through a potentiometer before the amplifier, which I suppose provides constant gain. But the circuit also has some capacitors, most probably treble bleed capacitors, which I suppose let some overdrive-level parts of the signal pass to the amp.

Do you think that attenuating my theremin signal will help? Suggestions on modifying the speaker circuit are also welcome (I can post pics of the speaker circuits if needed).

Posted: 4/18/2017 6:20:50 PM

From: Athens, Greece

Joined: 2/27/2017

Anyway, I shorted things out. The response of the speakers is not the cause of the noise. The source of the distorted sound was the interference of nearby high-voltage power lines to the theremin oscillators.

When I moved my setup to a different house, the problems were gone. Now these speakers render the sound of my theremin extremely well for a 30€ system. I should probably consider shielding my theremin circuit within a faraday-cage-like enclosure.

However, I report that these cheap speakers make for a quite decent choice if a better sound system is not available.


Best regards,


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